This invention relates to decreasing the permeability of a subterranean region, such as a region in or around a permeable earth formation that is encountered by the borehole of a well.
The need for decreasing the permeability of various subterranean regions has long been known and numerous processes have been proposed for doing so. For example, U.S. Pat. No. 3,195,630 describes an aqueous solution of urea and a salt of a metal from which a gel is formed; the T. J. Robichaux U.S. Pat. No. 3,308,884 describes an aromatic solvent solution of epoxy amino resin-forming components, which solution subsequently becomes a flow-resistant gel; and the H. J. Sommer, Jr. and W. C. Simpson U.S. Pat. No. 3,324,041 describes an emulsion that contains an asphalt, a polyamide, and a polyepoxy polymer, and subsequently becomes a highly viscous material; etc. The prior processes that are capable of plugging loose sands by converting them to consolidated, compression-resistant plugs tend to be undesirably expensive. The less costly prior processes that form gels or viscous fluids tend to fail in unconsolidated reservoir sands because the plugged portions of the sands are displaced into the well and/or to fail in reservoirs of low permeability because portions of the emulsions are too large to penetrate into the pores of the reservoir.